At a town hall meeting Friday in Texas, Sen. John McCain, R-Ariz., declared that "there's strong evidence" that thimerosal, a mercury-based preservative that was once in many childhood vaccines, is responsible for the increased diagnoses of autism in the U.S. -- a position in stark contrast with the view of the medical establishment.

McCain was responding to a question from the mother of a boy with autism, who asked about a recent story that the U.S. Court of Federal Claims and the National Vaccine Injury Compensation Program had issued a judgment in favor of an unnamed child whose family claimed regressive encephalopathy and symptoms of autism were caused by thimerosal. . . .

"We've been waiting for years for kind of a responsible answer to this question, and are hoping that you can help us out there," the woman said.

McCain said, per ABC News' Bret Hovell, that "It's indisputable that (autism) is on the rise amongst children, the question is what's causing it. And we go back and forth and there's strong evidence that indicates that it's got to do with a preservative in vaccines."

McCain said there's "divided scientific opinion" on the matter, with "many on the other side that are credible scientists that are saying that's not the cause of it."

The established medical community is not as divided as McCain made it sound, however. Overwhelmingly the "credible scientists," at least as the government and the medical establishment so ordain them, side against McCain's view.

Moreover, those scientists and organizations fear that powerful people lending credence to the thimerosal theory could dissuade parents from getting their children immunized -- which in their view would lead to a very real health crisis.

Tapper does a good job of exposing the scientific illiteracy of McCain's remarks. Here's more from Orac and Mark Kleiman. Orac also has background on the court case referenced in the story. And my co-blogger David Bernstein blogged on media coverage of thimerosal here.

On Monday I criticized Senator John McCain for giving credence to claims that vaccines are linked to the rise in autism diagnoses. Some believers in such a link point to the case of Hannah Polling, recently settled by the federal government, as evidence in support of their claims. Specifically, the government agreed that Polling's parents were entitled to compensation from the federcal vaccine injury compensation fund because vaccines "aggravated an underlying mitochondrial disorder, which predisposed her to deficits in cellular energy metabolism, and manifested as a regressive encephalopathy with features of autism spectrum disorder." Today's NYTreports on the case:

Advocates say the settlement — reached last fall in a federal compensation court for people injured by vaccines, but disclosed only in recent days — is a long-overdue government recognition that vaccinations can cause autism. . . .

Government officials say they have made no such concession.

"Let me be very clear that the government has made absolutely no statement indicating that vaccines are a cause of autism," Dr. Julie L. Gerberding, director of the Centers for Disease Control and Prevention, said Thursday. "That is a complete mischaracterization of the findings of the case and a complete mischaracterization of any of the science that we have at our disposal today." . . .

There are two theories about what happened to Hannah, said her mother, Terry Poling. The first is that she had an underlying mitochondrial disorder that vaccinations aggravated. The second is that vaccinations caused this disorder.

"The government chose to believe the first theory," Ms. Poling said, but added, "We don't know that she had an underlying disorder."

In a news conference on Thursday, Dr. Edwin Trevathan, director of the National Center for Birth Defects and Development Disabilities at the disease control agency, said, "I don't think we have any science that would lead us to believe that mitochondrial disorders are caused by vaccines."

The New York Timesreports on public health concerns about the growing number of parents who refuse vaccinations for their children.

Children who are not vaccinated are unnecessarily susceptible to serious illnesses, they say, but also present a danger to children who have had their shots — the measles vaccine, for instance, is only 95 percent effective — and to those children too young to receive certain vaccines.

Measles, almost wholly eradicated in the United States through vaccines, can cause pneumonia and brain swelling, which in rare cases can lead to death. The measles outbreak here alarmed public health officials, sickened babies and sent one child to the hospital.

Every state allows medical exemptions, and most permit exemptions based on religious practices. But an increasing number of the vaccine skeptics belong to a different group — those who object to the inoculations because of their personal beliefs, often related to an unproven notion that vaccines are linked to autism and other disorders.

Twenty states, including California, Ohio and Texas, allow some kind of personal exemption, according to a tally by the Johns Hopkins University. . . .

In 1991, less than 1 percent of children in the states with personal-belief exemptions went without vaccines based on the exemption; by 2004, the most recent year for which data are available, the percentage had increased to 2.54 percent, said Saad B. Omer, an assistant scientist at the Johns Hopkins Bloomberg School of Public Health.

While nationwide over 90 percent of children old enough to receive vaccines get them, the number of exemptions worries many health officials and experts. They say that vaccines have saved countless lives, and that personal-belief exemptions are potentially dangerous and bad public policy because they are not based on sound science.

"If you have clusters of exemptions, you increase the risk of exposing everyone in the community," said Dr. Omer, who has extensively studied disease outbreaks and vaccines.

It is the absence, or close to it, of some illnesses in the United States that keep some parents from opting for the shots. Worldwide, 242,000 children a year die from measles, but it used to be near one million. The deaths have dropped because of vaccination, a 68 percent decrease from 2000 to 2006.

"The very success of immunizations has turned out to be an Achilles' heel," said Dr. Mark Sawyer, a pediatrician and infectious disease specialist at Rady Children's Hospital in San Diego. "Most of these parents have never seen measles, and don't realize it could be a bad disease so they turn their concerns to unfounded risks. They do not perceive risk of the disease but perceive risk of the vaccine."

I find the following quote, from the article on vaccines linked to by Jonathan, below, horrifying:

In the wake of last month's outbreak, Linda Palmer considered sending her son to a measles party to contract the virus. Several years ago, the boy, now 12, contracted chicken pox when Ms. Palmer had him attend a gathering of children with that virus. "It is a very common thing in the natural-health oriented world," Ms. Palmer said of the parties.

I had chicken pox as a kid, and I remember it as a very unpleasant experience, to say the least, and I didn't have an especially severe outbreak. Measles, I take it, is worse and also more dangerous. Parents like Ms. Palmer are not only exposing their own children to horrible illnesses easily preventable by vaccines, but they are putting other children, including my own daughter, at risk, since the measles vaccine is only 95% effective. (And what about adults who either received an ineffective vaccine or immigrated from a country where vaccination was not universal)? A Ms. Carlson says, "I cannot deny that my child can put someone else at risk."

Without the externality of putting other people at risk, I think mandatory vaccination would be a close call. With it, I'd say that unless a parent is going to keep his children at home and not expose them to vaccinated children, make them get vaccines. Too unlibertarian for you? Make them pay a fine equal to the monetary value of the level of risk to others they're creating, to be used perhaps to subsidize vaccination programs for the poor, thus reducing the risks from elsewhere.